Field of the Invention
The present invention relates to a shake correction apparatus and to a control method therefor.
Description of the Related Art
There are an optical image shake correction processing and an imaging element image shake correction processing and the like, which serve as processing for correcting a shake (vibration) applied to an image pickup apparatus such as a still camera or a video camera from the outside. In the optical image shake correction processing, a shift lens (correction lens) is driven in a plane perpendicular to an optical axis. In the imaging element image shake correction processing, an imaging element is driven in the plane perpendicular to the optical axis. In the processing, the image pickup apparatus calculates an image shake correction amount by performing a cutoff of a predetermined frequency, and by performing a calculation that is centered on integration for matching an input/output unit, to a signal from a sensor for detecting a degree of the shake.
An angular velocity sensor is used for detecting a degree of the shake. The angular velocity sensor vibrates a vibration material such as a piezoelectric element at a constant frequency, and converts a force due to a Coriolis force that is generated by a rotary movement component into a voltage to obtain the angular velocity information. As shown in FIG. 10, a vertical direction (Pitch) and a horizontal direction (Yaw) are commonly used, which serve as directions for detecting the shake when the image pickup apparatus is located at a center of an orthogonal coordinate system.
In the optical image shake correction processing, a shake of an image (image shake) formed on the imaging element is removed by moving the shift lens, which moves in the plane perpendicular to the optical axis, serving as a correction means for correcting the image shake. In contrast, in the imaging element image shake processing, the shake of an image is removed from the image by moving the imaging element that serves as the correction means for correcting the image shake and moves in the plane perpendicular to the optical axis by the image shake correction amount. An explanation is provided of an example of a configuration of the optical image shake correction processing as below.
The image pickup apparatus for correcting the shake by using the optical image shake correction processing, firstly, commands a movement by the image shake correction amount to a shift lens driving unit, and obtains an actual position of the shift lens so that the shift lens that is a control target can be driven to a targeted value. Secondly, the image pickup apparatus executes feedback control, for example, PID control, so as to make a deviation between the target value and the actual position zero.
Desirable characteristics for the correction mechanism are, for example, an excellent tracking to a target with low friction, and an easy operability regarding a resonance frequency for a designer. As a mechanism for accomplishing the characteristics, Japanese Patent Laid-Open No. 2001-290184 discloses a shake correction mechanism for interposing a plurality of balls between a movable barrel and a fixed barrel and pressing by an elastic body.
In the shake correction mechanism disclosed in Japanese Patent Laid-Open No. 2001-290184, it is desirable that the ball is always in a rolling state because the tracking decreases according to the shift to the sliding friction of the ball while the ball contacts an end surface of a ball receiving unit. Accordingly, Japanese Patent Laid-Open No. 2001-290184 discloses that the movable barrel is moved by the maximum moving amount or the actual moving amount in advance, and initialization driving of the shift lens is performed.
Further, Japanese Patent Laid-Open No. H5-215992 discloses that the shake correction mechanism for extracting a signal in a gravity direction from a shake correction driving means and for detecting an attitude of the image pickup apparatus. Furthermore, Japanese Patent Laid-Open No. 2000-312329 discloses an image processing apparatus for detecting an attitude condition of the image processing apparatus during photographing, recording information of the attitude condition with photographing image data that is obtained by the photographing, and performing a rotation process of the photographing image data based on the attitude condition.
In the shake correction mechanism disclosed in Japanese Patent Laid-Open No. 2001-290184, the initialization operations of the shift lens during a start-up of the apparatus are same in each time. That is, the shake correction mechanism moves the shift lens by the maximum moving amount each time. However, if it is attempted to move the shift lens within a possible shortest time, a driving sound of the shift lens becomes large. When the driving sound of the shift lens becomes large, a harsh sound is generated each time at the start-up of the shift lens, and as a result, an the user has an uncomfortable feeling. While it is desirable that the driving sound of the shift lens is small, driving time of the shift lens influences the time between a start-up of a power source of the image pickup apparatus and a start-up of a system capable of performing photographing. Accordingly, if the initialization driving is performed for a long time, the time between the pressing of a power button and an available timing of the photographing is prolonged, and as a result, an the user has uncomfortable feeling.
In addition, an image pickup apparatus having a structure in which a lens barrel having, for example, a zoom lens and the shift lens, a focus lens, and an aperture/shutter unit is allowed to change the total length between an extended state (a state capable of photographing) and a collapsed state (a state that the barrel is accommodated when the photographing is not performed), is presumed.
In a case where the image pickup apparatus is set to the start-up mode where the lens barrel remains in the collapsed state during the start-up (for example, a play start-up mode enabling only a function for displaying the photographing image on a display unit such as an LCD), the sound is conspicuous if the sound caused by the initialization operation of the shift lens is large. In addition, in a case where the initialization operation time is prolonged for reducing the sound volume, the start-up time is prolonged.